After serving his guest at Tokyo's most celebrated sushi restaurant, Japanese Prime Minister Shinzo Abe finally got a long-awaited commitment from US President Barack Obama.

By applying a US-Japan security treaty to the Diaoyu islands, Obama has reassured its anxious Japanese ally, who started a bitter territorial dispute with China by nationalizing the East China Sea islands in 2012.

But it would be premature and simply naive of Tokyo to draw any convenient conclusions from the pledge and convince itself Washington will support it at any cost, even in a war caused by its provocation.

At a joint press conference with Abe Thursday, Obama said the Diaoyu islands were covered by the defense treaty that obliges Washington to act if Japan is attacked.

This is a standard US policy, a political cliche, the meaning of which should not be exaggerated. As Obama explained: "This is not a new position."

However, what is extremely dangerous is that Abe and his nationalistic government might be encouraged to challenge China's bottom line in territorial disputes in the belief that Obama's pledge is a shield that gives them immunity from all punishments.

Unfortunately, it is just another typical Tokyo illusion. Shortly after this commitment, Obama refused to draw a "red line" on China-Japan territorial disputes by saying his government took no side on the issue, and shied away from the question of whether America will intervene militarily if an armed incursion targeting the disputed islands happens.

He further disappointed some pugnacious Japanese politicians by calling for peaceful solutions to the disputes in the region through dialogue, an approach with which China could not agree more.

China's stance on the Diaoyu islands is consistent and clear: these islands are an inherent part of Chinese territory and China holds indisputable sovereignty over them.

Japan's occupation of the islands are illegal and invalid. The US-Japan defense treaty, an anachronism of the Cold War, cannot undermine China's territorial sovereignty and legitimate rights.

Both Japan and the US should not underestimate China's determination to safeguard national territorial sovereignty and maritime interests.

Therefore, the United States, a responsible and reliable partner as it claims, should respect facts, take a responsible attitude, and honor its commitment of not taking a position on this issue.

Instead of ratcheting up support for its recidivous trouble-making ally, the US should help Tokyo reduce its hotheadedness and provide "off-ramps" that could steer Japan toward detente with China.

The United States should be cautious with its words and deeds if it really wants to play a constructive role in regional peace and stability. After all, Tokyo has already become a growing liability to Washington's pursuit of its long-term interests.